The present invention relates to the field of electronic design automation. More specifically, the present invention relates to electronic design automation including lithography aware leakage and timing analysis.
Leakage has become a primary concern in the consumption of power in semiconductor chips. Timing also is a concern because it drives the capability of the circuitry to make the calculations rapidly enough to meet customer's requirements.
Historically power and timing were deterministically calculated often considering worst case analysis. Over time it has become obvious that deterministic calculation results in insufficient yield, especially as each individual circuit component is considered from a worst case perspective. Instead, statistical analysis may be used, realizing that a range of operation distribution exists for which most of the distribution well meets customer requirements. This statistical analysis has come to be used on both timing analysis and more recently on leakage analysis.
Leakage is a function of the overall transistor gate width in a given circuit. Low threshold voltage FETs have significantly higher leakage and correspondingly higher performance. For multi-threshold voltage processes there are typically two levels. A low threshold (VT) device for high performance and a normal threshold device for lower power and lower performance. By selectively utilizing low threshold devices only where needed, the performance requirement is met while keeping the power consumption relatively low. One method to approximate leakage current which will be utilized by the chip is by totaling the cumulative FET gate width for each threshold device.
There are systematic variations and random variations which affect timing and power. An example of a systematic variation would be lithography defocus since this is a controllable parameter that affects the entire chip. A random variation would be due to a change in the number of dopant molecules since these can vary on a transistor by transistor basis. These variations impact the overall design and can be used statistically to tune the design to meet timing and leakage requirements.
Accordingly, what is desired are improved methods and apparatus for solving the problems discussed above. Additionally, what is desired are improved methods and apparatus for reducing some of the drawbacks discussed above.